1. Field of Invention
This invention relates to working mechanisms for treatment tables and more particularly to pneumatic type working mechanisms for moving a treatment table.
2. Prior Art
In conventional treatment tables, the working mechanisms for the purpose of raising and lowering the treatment table bed or laying down and putting up the backboard of the treatment table or bed are roughly classified into two species. One of the species is the screw jack-system working mechanism in which the raising and lowering motion is effected by the rotation of a screw rod driven by an electric motor. The other is a hydraulic working mechanism which causes the raising motion by feeding oil into a hydraulic cylinder from a hydraulic pump which is direct coupled to a motor and which brings about the stopping and raising and lowering motions by means of an electromagnetic valve and the like provided in the oil pressure circuit.
There are many controversial points, however, in the utilization of such kinds of working mechanisms as described below. Namely, there is a fear of deterioration of the electric insulating parts during the course of a long time which would result in electric leakage or shock and in particular this is an acute problem for dental use wherein the table is very likely to be located very near to a water circuit. Secondly, in order to prevent a accidental electric leakage or shock, frequent inspection and subsequent replacement of insulating parts is necessary and this results in a considerable loss of time and expenditure required for such inspection and replacement. Thirdly, vibration and noise brought about by the rotation of the motor give an offensive sensation to both the doctor and the patient and in particular the screw-jack type working mechanism causes a greater discomfort as a result of jars created by the grating jack. Fourthly, in hydraulic working mechanisms it is feared that oil leakage will occur which will cause a decrease in the oil pressure or oil stains on the floor of the office wherein the treatment table is located. Fifthly, if such mechanisms are exported world wide, it would be very often required to change the design of the motors according to the rated voltage of the country of destination.
To overcome the above difficulties, it has been considered to replace the hydraulic cylinder with a gas pressure cylinder. Such a system while solving some of the above problems creates problems of its own. Such problems include that the gas pressure cylinder must be larger than the oil pressure cylinder which results in a larger table size; the gas pressure cylinder results in a larger stopping shock; the actual stopping position of the treatment table is at some significant distance past the desired position; and the pneumatic cylinder makes allowed exhaust sound.